1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier and a printer, and in particular, an image forming apparatus in which a cooling mechanism is used which takes radiated heat out of a power source board.
2. Description of the Related Art
FIG. 5 shows the configuration of a conventional image forming apparatus. Reference numeral 100 denotes such an image forming apparatus, and herein, as an example, a digital multi-function machine is shown. In this image forming apparatus 100, when a copying operation is executes, in an image forming portion 2 inside of a main body 1, a photosensitive drum 4 which rotates clockwise (i.e., in the direction indicated by the arrow in the figure) is uniformly charged with electricity by a charging unit 3. Then, a laser beam from an exposure unit 8 (such as a laser scanning unit) based on original image data which is read by an image reading portion 5 forms an electrostatic latent image on the photosensitive drum 4. A development unit 7 allows a developer (hereinafter, referred to as the toner) to adhere to this electrostatic latent image, so that a toner image is formed. This development unit 7 is supplied with the toner from a toner container 6.
Toward the photosensitive drum 4 on which the toner image is formed as described above, sheet 9 is conveyed from a sheet feed mechanism 10 via a sheet feed roller 11, a sheet conveying path 12 and a registration roller pair 13 to the image forming portion 2. In this image forming portion 2, a transfer roller 14 transfers, to the sheet 9, the toner image formed on the surface of the photosensitive drum 4. The sheet 9 to which the toner image has been transferred is detached from the photosensitive drum 4. Then, it is conveyed to a fixation unit 15 to fix the toner image. The toner (i.e., residual toner) which remains on the surface of the photosensitive drum 4 after the toner image has been transferred to the sheet 9 is removed by a cleaning unit 16.
The sheet 9 which has passed through the fixation unit 15 is conveyed to a branching member 17, and in the branching member 17, its conveying direction is divided into several directions. If the image is formed only on one surface of the sheet 9, then with the image surface kept upward (which is called face-up), the sheet 9 passes through a side discharge-roller pair 18 and is discharged from a side outlet 25 onto a sheet discharge tray 19. Or, it is sorted to a sheet conveying path 20 by the branching member 17 and passes through a conveying roller pair 21. By a inner discharge-roller pair 22, it is discharged onto a inner discharge tray 23 with the image surface turned downward (which is called face-down). The sheet conveying path 20, the conveying roller pair 21 and the inner discharge-roller pair 22 also function as a switchback unit which changes the sheet 9's conveying direction.
On the other hand, if the image is formed on both surfaces of the sheet 9, the sheet 9 which has passed through the fixation unit 15 is allocated to the sheet conveying path 20 by the branching member 17. Then, after its rear-end part has passed through the branching member 17, the conveying roller pair 21 and the inner discharge-roller pair 22 are reversely rotated to change the conveying direction. Thereafter, in the branching member 17, the sheet 9 is sorted to a duplex printing path 24 this time. Thus, the surface on which the image is not formed is turned upward and conveyed again to the image forming portion 2. On the sheet 9 conveyed again, the next image is formed in the image forming portion 2. Then, it is conveyed to the fixation unit 15 to fix the toner image. Thereafter, it is discharged outside of the apparatus from the side discharge-roller pair 18 or the inner discharge-roller pair 22.
In addition, an electric-charge elimination unit (not shown) which eliminates a residual electric charge remaining on the surface of the photosensitive drum 4 is provided on the downstream side of the cleaning unit 16. Besides, the sheet feed mechanism 10 is fit to the main body 1 so that it can be freely attached and detached. It is made up of a plurality of sheet feed cassettes 10a, 10b, 10c which store sheets, and a by-pass stack (or a manual tray) 10d which is provided above them. These are connected via the sheet conveying path 12 to the image forming portion 2 which is formed by the photosensitive drum 4, the development unit 7 and the like.
In the image forming apparatus 100 like this, a high-voltage power source board 26 for applying a high voltage to each component for the formation of an image, for example, as shown in FIG. 5, is opposite to the image forming portion 2 so as to cross a partition member (not shown) which is a part of the sheet conveying path 12. In the high-voltage power source board, there is disposed a heat-radiating component (not shown) such as a transformer. Hence, such a heat-radiating component needs to be cooled. In this respect, conventionally, for example, Japanese Patent Laid-Open No. 2004-93708 specification suggests a cooling mechanism which cools a heat-radiating component disposed on such a power source board. As this cooling mechanism, an air outlet is formed in the surface of a side plate of a body frame, and in the position of this air outlet, a cooling fan is provided which discharges the air heated up by the heat generated from components which radiate a large quantity of heat.
However, if such a cooling fan is provided in the body frame's side plate, a disadvantage arises in that an image forming apparatus becomes larger. Besides, if the cooling fan is disposed in the side plate, the distance becomes longer between the cooling fan and a heat-radiating component to be cooled on a high-voltage power source board. This makes it difficult to form an air-flow path or do another such. Hence, another disadvantage is also raised in that it cannot be efficiently cooled.